I believe with the latest version of Virtualmin & Ubuntu as you propose you will have MariaDB not MySQL (with the option to add Postgre or not).
So hopefully that works well for you.
The Virtualmin 7 installer (now the one you get when you click the link at Downloading and Installing Virtualmin – Virtualmin) will install Mariadb on all supported platforms by default. You can switch easily after installation (but before adding any databases), if you want to…but you almost certainly should not want to. There is no compelling technical reason to choose MySQL over MariaDB, and MariaDB has the preponderance of community support at this point.